Sure, why not.
1) They are being used as satellite dishes in Yugoslavia.
2) They are really flying saucers that were spuing on us. Now that they have collected enough data and flown back to the mother ship, expect an invasion any day.
3) They haven’t been stolen. Global warming caused the holes to expand, and the covers simply fell in.
4) Papa John’s ran out of pizza trays.
5) A giant magnetic asteroid passed by and sucked them all up.
6) A previously unknown race of giants is using them to play checkers.
7) Occupy Wall Streeters decided that the 1% didn’t deserve manhole covers.
8) The DOT did it, thinking that unrepaired potholes would look small by comparison.
9) It’s all a vast right-wing conspiracy.
10) The U.S. Olympic squad ran out of practice discuses.
11) Mayor Bloomberg took ’em out. They slow traffic better than speed bumps.